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Pi TFT 2.8" slows down and is noisy with 20140917-1 bootload
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Pi TFT 2.8" slows down and is noisy with 20140917-1 bootload

by DozenCrows on Sun Nov 16, 2014 4:48 pm

I upgraded the bootloader package to the above version in a project that uses the 2.8" resistive TFT touch screen for Raspberry Pi, and noticed two things:
  • Display update is significantly slower.
  • Display update causes audible noise on speakers attached via a USB audio dongle.
If I roll back to the bootloader package raspberrypi-bootloader-adafruit-20140421-3.deb, both of these problems go away.

I've attached dmesg output for both cases.

Please would you advise me on this; I would like to use the updated bootloader as the firmware/kernel it contains fixes a different issue (not related to display), but the loss of performance and the added noise are not acceptable for my project.
Attachments
dmesg-20140421-3.log
(13.16 KiB) Downloaded 16 times
dmesg-20140917-1.log
(14.21 KiB) Downloaded 15 times

DozenCrows
 
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Re: Pi TFT 2.8" slows down and is noisy with 20140917-1 boot

by adafruit2 on Mon Nov 17, 2014 1:33 pm

Hiya, looks like the 917 log is:
[ 13.208067] graphics fb1: fb_ili9340 frame buffer, 320x240, 150 KiB video memory, 4 KiB DMA buffer memory, fps=20, spi0.0 at 32 MHz


and the 421 log is:
[ 12.216710] graphics fb1: fb_ili9340 frame buffer, 320x240, 150 KiB video memory, 4 KiB DMA buffer memory, fps=20, spi0.0 at 32 MHz


which is the same :/ so we dont know why screen updates would be different. So we don't have any advice - according to the kernel, both are updating at the exact same rate using the same DMA buffer size!

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Re: Pi TFT 2.8" slows down and is noisy with 20140917-1 boot

by DozenCrows on Sat Nov 29, 2014 9:41 am

Many thanks for checking the logs.

One thing I did notice is that the 017 log for the most recent bootloader has two extra lines regarding the SPI module:
[ 12.182517] fbtft_device: Deleting spi0.1 (spi0.1)

and
[ 12.219806] fbtft_device: Deleting spi0.0 (spi0.0)

which are the SPI devices for stmpe610 and fb_ili9340. Could that be important?

I've also tested the two different bootloaders on a different Pi, running a different project with another TFT of the same model, and am seeing a 10% slowdown when profiling the screen update.

Please would it be possible for you to try and see if you can replicate this...or not? I appreciate that the original TFT code comes from a third party, and that the bootloader package contains a complete kernel - but knowing if this performance and noise issue can be found by someone else independently is useful for working out how to resolve this. Note that you have to use a model B rather than a B+, as the 0421 bootloader predates the B+.

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Re: Pi TFT 2.8" slows down and is noisy with 20140917-1 boot

by DozenCrows on Sun Nov 30, 2014 5:06 pm

Looks like others may have run into something similar: http://forums.adafruit.com/viewtopic.php?f=47&t=63696

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